The invention relates to a sensor device for a disc brake, in particular for a motor vehicle, having a sensor gearing which is coupleable to at least one encoder. The invention also relates to a disc brake having a sensor device of this type.
Sensor devices of this type are used for detecting a state of wear of brake pads and a brake disc of a disc brake. Furthermore, sensor devices are also used for the detection of an actuation stroke of a brake-application apparatus of a disc brake, in order thereby to determine a present air gap.
Disc brakes of this type are commonly actuated by way of compressed air and equipped with automatically acting, mechanical wear-compensating readjustment apparatuses. This wear-compensating readjustment apparatuses operate in a very reliable manner and decrease the size of an air gap that has become too large. They are known in various embodiments, such as for example mechanical readjusters with automatic regulation of a friction point. Here, the readjustment apparatus is activated during every brake actuation, for example by way of an advancing element of a brake-application apparatus of the disc brake. In the event of wear of brake pads and brake disc, an automatic readjustment of the pads is performed by way of the wear-compensating readjustment apparatus, for example by way of an adjustment movement of threaded tubes that are variable in length.
An example of a readjustment apparatus is described in DE 10 2004 037 771 A1. Here, a drive rotational movement is transmitted for example from a torque limiting device, for example with a ball ramp, via a continuously acting clutch (slip clutch) to an adjustment spindle of a threaded tube.
For detection of the wear, it is possible for a linear movement of a readjustment element to be directly detected. The readjustment element, for example a readjustment spindle, performs the entire actuation stroke and the readjustment travel. An example of this is illustrated in EP 1 892 435 B1. Here, it is considered to be a disadvantage that the actuation stroke is considerably smaller than the wear travel. Numerical examples in the case of a conventional brake are, for example, an actuation stroke of approximately 4.5 mm and a readjustment travel of approximately 60 mm.
A measurement encoder must therefore simultaneously have a large measurement range and a high resolution. Since these characteristics are generally contradictory, this leads to an expensive sensor. Furthermore, the transmission to a vehicle control system is made more difficult. A presently common interface from a brake to a vehicle control system is an analog transmission in the case of which an electric voltage in relation to a common ground corresponds to the measurement value. Since the readjustment travel determines the amplitude of the transmission signal, the signal amplitude will, owing to the actuation stroke, exhibit the same relationship as a maximum actuation stroke to a maximum wear travel. In this regard, a numerical example of the abovementioned conventional brake will be specified. The voltage amplitude is 2.5 V. In the case of a wear travel of 60 mm, the characteristic curve of the sensor must therefore be designed for 2.5 V/60 mm=47.7 V/m in order to cover the entire measurement range. If one assumes noise with an amplitude of 20 mV, the actuation stroke can thus be determined at best with an accuracy of 0.48 mm. An air gap is generally in a size range of 0.5 . . . 1.2 mm, and is very difficult to determine in this way.
One possibility for circumventing the problem discussed above lies in the use of a separate linear sensor or of a rotation sensor for the actuation stroke. The second sensor may then exhibit a higher resolution in a smaller measurement range. A disadvantage here is the outlay in terms of parts, with associated work outlay, owing to the additional sensor, additional lines or signal processing electronics for the electrical transmission of the two signals.
DE 102010032515 A1 describes a brake wear sensor of a disc brake. Here, a superposition of readjustment travel and actuation stroke is realized by way of a planetary gearing. The readjustment travel is introduced as a rotational movement into the sun gear of the planetary gearing. For example, the rotational movement of a readjustment spindle is expedient for this purpose. The actuation stroke is introduced as a further rotational movement via the planet carrier of the planetary gearing. The rotation of the internal gear of the planetary gearing is detected by way of a suitable encoder, for example a Hall sensor, a potentiometer, an inductive, optical or acoustic encoder element. In this way, it is possible to realize a transmission ratio of the readjustment movement in the range of for example 10, and a transmission ratio of the actuation stroke in the range of for example 1. Thus, on the internal gear, deflection amplitudes in the same magnitude range arise owing to the two input variables, and can be used with the encoder with a measurement range adapted to the required resolution.
Owing to the ever-increasing demand to reduce the number of parts and therefore costs, wherein at the same time quality and benefit should be not only maintained but increased and furthermore, increased capability for adaptation to different usage conditions is demanded, there is a corresponding requirement for an improved sensor device.
It is the object of the present invention to provide an improved sensor device. It is a further object to provide an improved disc brake.
The object is achieved by way of a sensor device, as well as a disc brake having the sensor device, in accordance with embodiments of the invention.
A sensor device is provided which, in terms of its construction, can be easily converted for different tasks using a small number of parts. In this way, it is for example possible for an amount of stock to be reduced and to still be easily and quickly converted for different purposes shortly before use.
A sensor device according to the invention for a disc brake has a sensor gearing which is couplable to at least one encoder, wherein the sensor gearing is arranged in a housing as a planetary gearing and has an input for a first variable to be detected by the sensor device, which first variable is associated with wear of the disc brake, and an input for a second variable to be detected by the sensor device, which second variable is associated with an actuation stroke of the disc brake. The sensor device is capable of being converted from a first state, for detecting the first variable which is associated with wear of the disc brake and detecting the second variable which is associated with an actuation stroke of the disc brake, into a second state, for detecting only the first variable which is associated with wear of the disc brake.
A disc brake according to the invention, in particular for a motor vehicle, having a brake-application apparatus with a spreading mechanism, preferably with a brake rotary lever, and a wear-compensating readjustment apparatus which has at least one mechanical readjustment device which is preferably insertable into a spindle unit of the disc brake and coupled to the spreading mechanism, preferably to the brake rotary lever, is equipped with a sensor device according to the invention. The input of the sensor gearing of the sensor device for the first variable to be detected is coupled to the at least one mechanical readjustment device, and the input of the sensor gearing of the sensor device for the second variable to be detected is coupled to the spreading mechanism, preferably to the brake rotary lever, by way of a stroke sensor drive.
In this way, it is made possible for the actuation stroke, which is a linear movement aside from the pivoting movement of a bridge of the disc brake, to be converted into a rotational or pivoting movement and transmitted to the second input of the sensor gearing.
In this embodiment of the sensor device, the sensor gearing is equipped with an interface for the coupling of an encoder. The interface may for example be a rotationally fixed plug-type connection. In this way, retroactive assembly is made possible even with different encoders.
The spreading mechanism, preferably the brake rotary lever, drives two drives, specifically firstly the readjustment device and secondly the stroke sensor drive.
In one embodiment, the input of the sensor gearing for the first variable to be detected is a sun gear of the sensor gearing, and an input for the second variable to be detected is a planet carrier of the sensor gearing with a planet carrier toothing. The planetary gearing serves as a single sensor gearing for the superposition of both input variables, and can be used without itself being modified.
In a further embodiment, in the first state of the sensor device, the input for the second variable to be detected is in engagement with a stroke sensor drive unit, and in the second state of the sensor device, the input is blocked. In this way, a simple adaptation to the two states is possible by way of a conversion.
Here, the stroke sensor drive unit has at least one toothed gear which, in the first state of the sensor device, engages with the planet carrier toothing, which is an external toothing, in an opening of the housing. With the at least one toothed gear, a transmission with a particular transmission ratio is possible, whereby the subsequent rotation of the internal gear owing to the actuation stroke can be coordinated with the rotation of the internal gear owing to the readjustment, that is to say by the first input. The transmission may be performed with a small amount of play, wherein the actuation stroke can be detected with high accuracy and a high resolution, in contrast to the prior art.
Furthermore, the pivoting of the brake rotary lever, which is for example in the form of an eccentric lever, may be used for introducing the actuation stroke as a pivoting/rotational movement into the planetary gearing. The problem whereby the pivot axes of the brake rotary lever and readjustment spindle or sensor axis of the sensor device do not lie in a plane and have an axial offset is solved by way of the toothed gear, wherein the axial offset is compensated in a simple manner. This is advantageous because the axial offset is a result of the design of the brake rotary lever as an eccentric lever, and, for structural space reasons, cannot be compensated.
In a further embodiment, it is provided that the at least one toothed gear is rotatably mounted, and axially delimited, in a bracket and in the housing. Thus, simple enhancement and installation of the toothed gear is made possible.
If the bracket is fastenable in removable fashion to the housing, the toothed gear can be installed quickly.
In another embodiment, the input for the second variable to be detected is, in the second state of the sensor device, rotationally fixedly blocked by at least one fixing tooth of a bracket which is connected rotationally fixedly to the housing, wherein the at least one fixing tooth is in engagement with the planet carrier toothing, which is an external toothing, in an opening of the housing. Thus, an existing toothed gear with bracket can be easily and quickly exchanged for a bracket with integrated fixing toothing, whereby a quick conversion is possible.
Reversible conversion is possible if the bracket is fastenable in removable fashion to the housing.
In an alternative embodiment, the input of the sensor gearing for the first variable to be detected is a drive shaft with at least one gearing stage which is coupled to a sun gear of the sensor gearing, and an input for the second variable to be detected is a planet carrier of the sensor gearing with a planet carrier toothing. The abovementioned axial offset is in this case compensated by the spacing of drive shaft and sun gear. The sensor gearing can, however, maintain its space requirement.
It is furthermore provided that, in the first state of the sensor device, the input for the second variable to be detected is in engagement with a stroke sensor drive unit or is provided for direct engagement of a stroke sensor actuator of an associated disc brake. In the second state of the sensor device, the input is blocked. Since the lever pivot axis and the axis of the input, that is to say of the planet carrier, lie in one plane, the stroke sensor actuator can engage directly with the planet carrier. It is self-evidently also possible for one or more gearing stages to be interposed.
In another embodiment, in the second state of the sensor device, the input for the second variable to be detected is rotationally fixedly blocked by at least one fixing arm, wherein the at least one fixing arm is in engagement with the planet carrier toothing, which is an external toothing. For a quick conversion, the at least one fixing arm may be fastenable in removable fashion to the housing. Thus, reversible conversion is possible. An irreversible conversion is self-evidently also possible if the at least one fixing arm is connected severably to the housing by way of a predetermined breaking section.
It is advantageous if the at least one fixing arm, in the form of an insert part, is insertable rotationally fixedly into, and removable from, the housing, because a simple and quick reversible conversion is possible in this way.
In a further embodiment, the above sensor device has at least one encoder which is coupled to the sensor gearing. The sensor device may thus be formed as a preassembled structural unit together with an encoder.
A disc brake is formed with at least two spindle units, wherein the at least one mechanical readjustment device is coupled to a driver by way of a synchronization unit. Here, the input of the sensor gearing of the sensor device for the first variable to be detected is coupled to a driver shaft of the driver. Effective structural space utilization is made possible in this way.
Owing to the right-angled arrangement of the lever pivot axis and axis of rotation of the readjustment spindle, the stroke sensor drive has an angular gearing. An angular gearing is, with few exceptions, considerably more sensitive to tolerances than a spur gear mechanism.
In another embodiment, the axial offset between a plane of a lever pivot axis of the brake rotary lever and a plane of a sensor axis of the sensor device is compensated by way of at least one gearing stage of the stroke sensor drive unit. Accordingly, an angular gearing, even with a crown toothing, is possible. The crown gear toothing is relatively insensitive with regard to position tolerances. Also self-evidently possible is, for example, a hypoid gearing, wherein a sensitivity with regard to position tolerances is increased, and quality control could be made more cumbersome.
In an alternative embodiment, the sensor device is arranged in the disc brake such that an axial offset between a plane of a lever pivot axis of the brake rotary lever, in which a sensor axis of the sensor device lies, and a plane of an axis of a spindle unit is compensated by at least one gearing stage of a drive shaft which is an input of the sensor gearing of the sensor device for the first variable to be detected. Here, the stroke sensor actuator, for example with a crown gear toothing, may interact directly with the planet carrier, or else with the internal gear.
The disc brake may also be actuated by compressed air.
For realization of variants of the sensor device, it is particularly advantageous for as many identical parts as possible to be able to be used, and for only very few parts to be required for conversion purposes. In the prior art, a variant only with readjustment travel detection can be realized only by virtue of the planet carrier being fixed.
By contrast, by replacing the toothed gear with a fixing component, that is to say with the bracket with integrated fixing tooth, the sensor variant without actuation stroke detection can be easily, even reversibly, converted. The number of identical parts is particularly advantageously high.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.